I would never suggest photoshopped receipts as this is fraud. However, will your credit card statement suffice since it will show the date/location/amount you spent. Sure, it could have been $30 in drinks or whatever, but it's worth a shot. Otherwise, I'd say to do a charge back. If it works, great. Otherwise, bit the bullet and learn the lesson of keeping receipts.

As an aside, I now use the SpeedPass app for fill-ups whenever possible. The receipt is emailed so it's always available for expenses, times like this when a receipt is lost, or when the machine outside doesn't print and you don't want to go inside and ask for one.